There has been proposed a technique wherein, in forming a p/n column structure by trench filling epitaxial growth, a mixed growth scheme based on an etching gas and silane gas is employed, thereby to prevent the open part of a trench from being closed earlier (refer to U.S. Pat. No. 7,029,977-B2).
Due to the mixing of the etching gas, however, the etching reaction of an n+-type silicon substrate occurs to give rise to the phenomenon that, as shown in FIG. 24, a high-concentration dopant (As, Sb or P) within the etched n+ substrate adheres onto the front surface of this substrate so as to be accepted into a p/n column layer. Meanwhile, a super junction MOS (SJ-MOS) overcomes the trade-of f relation of an ON-state resistance and a breakdown voltage by full depletion within a p/n column. It is required for the full depletion to balance the charge quantities of p/n column elements, and the mixing of the dopant from the n+ substrate is a fatal problem in a concentration design.
Further, a technique which is intended to perform trench filling by employing the etching action of an etching gas is disclosed in U.S. Pat. No. 6,495,294. Here, a trench shape tapered and worked by employing the etching action of the etching gas. Also in this case, a high-concentration dopant similarly adheres onto the front surface of an n+-type substrate (onto an epitaxial film of the opposite conductivity type within a trench) due to the etching reaction of the substrate.
Thus, it is required that a desired carrier distribution can be attained in a semiconductor substrate wherein trenches are formed in an epitaxial film on a silicon substrate and wherein other epitaxial films opposite in conductivity type to the first-mentioned epitaxial film are filled in the trenches.